1. Field of the Invention
In general terms, the invention relates to all multistage pumps using a long rotor equipped with blades and in particular axial or helico-axial pumps used for pumping two-phase effluents. Reference is made to the pumping of the fluid constituted by a mixture of oil and oil gas in connection with the exploitation of oil fields and in particular ocean fields.
2. Description of the Related Art
In a recent process for the exploitation of ocean fields, the effluents, which contain both liquid and gaseous oil, are not treated on a platform installed in the immediate vicinity, but are instead discharged to the side or to a platform located at some distance therefrom. As these effluents are formed by a multiphase fluid, it is necessary to have power pump units able to discharge from a field several dozen m.sup.3 of effluents every hour.
For this purpose use is made of two-phase multistage pumps which can be associated with a motor unit, with a view to permitting the discharge with a high flow rate of a two-phase or multiphase fluid such as oil effluents.
With reference to FIG. 2, these pumps are constituted by a rotor having a main shaft 100 to which are fixed pulsating systems 102. As can be seen in FIG. 2, each pulsating system 102 is fixed by means of a key 106 introduced into a slot formed for this purpose in the main shaft 100. This leads to a precise adjustment of the machining of the internal diameter of the pulsating system 102 with respect to the external diameter of the shaft 100, which is relatively expensive. As a result the rotor can be dismantled, but this makes the rotor difficult to balance after each pulsating system change. The invention aims at obviating this disadvantage by proposing a multistage pump with a different design with respect to the rotor.